Heat exchanger devices and systems and associated methods

ABSTRACT

Systems and methods for improved heat exchange performance are disclosed. The system can include a first slab of refrigerant tubes having an upstream side and a downstream side. The system can further include a second slab of refrigerant tubes having an upstream side and a downstream side. The system can additionally include an airflow distribution device configured to distribute air along the first and second slabs. Further, the downstream side of first slab can be set apart a first distance from the downstream side of the second slab and the upstream side of the first slab can be attached to the upstream side of the second slab. The airflow distribution device can include a perforated plate having perforations of various dimensions or various sized vanes positioned in the path of airflow.

FIELD OF THE TECHNOLOGY

The presently disclosed subject matter generally relates to improved heat exchanger devices and systems, and more specifically, to heat exchanger devices and systems incorporating configurations and mechanisms to improve air distribution along the heat exchanger tubes.

BACKGROUND

Heat exchangers are used in heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems. Heat exchangers generally include tubes for flowing refrigerant through the heat exchanger. Each tube may contain several individual flow channels, or paths. Fins may be positioned between the tubes to facilitate heat transfer between refrigerant contained within the flow paths and an external fluid passing over the tubes. Moreover, heat exchangers may be used in small tonnage systems, such as residential systems, or in large tonnage systems, such as industrial chiller systems.

FIG. 1 depicts an example of a prior art heat exchanger system 100. The system 100 can include an inlet duct 110, a heat exchanger 120, a blower 130, and an outlet duct 140. The transfer of heat within heat exchanger systems 100 is generally driven by flow of an external fluid passing through the heat exchanger 120. Typically, as the fluid passes through the heat exchanger 120 (i.e., over the slabs 122 a, 122 b, 122 c), the fluid contacts the individual tubes and flows across each tube (also called heat exchange tubes or HX tubes). Heat transfer between the external fluid and the refrigerant is dependent on, among other things, the temperature difference between the external fluid flowing across the tubes and the refrigerant flowing inside the tubes.

In order to provide the maximum possible surface area for heat exchange, heat exchangers and fan coils are often made up of two or more generally planar heat exchanger subassemblies, commonly referred to as slabs, which generally have their planes oriented obliquely with respect to the direction of air flow and which, together, occupy the height and width of the duct within which they are located. FIG. 2A depicts a configuration, known as an “N coil,” having three slabs 122 a, 122 b, 122 c formed into an N- or Z-shaped slab assembly having a first apex that points upstream and a second apex which points downstream. As shown, the first slab 122 a can include one or more tubes 205 a, 205 b, 205 c, the second slab 122 b can include one or more tubes 210 a, 210 b, and 210 c, and the third slab 122 c can include one or more tubes 215 a, 21 b, 215 c. FIG. 2B depicts a configuration, known as an “A coil,” having two slabs 122 a, 122 b formed into an A- or V-shaped slab assembly the apex of which points either upstream into or downstream from the air flow. As shown, the first slab 122 a can include one or more tubes 220 a, 220 b, 220 c and the second slab 122 b can include one or more tubes 225 a, 225 b, and 225 c.

FIG. 3A is a visual depiction of airflow through a prior art heat exchanger system 100. As shown, the airflow was lower in bottom region 310 of the heat exchanger 120. Further, as depicted in FIG. 3B, while the upper portion of the heat exchanger 120 receives as much as 40% of the airflow, the bottom region 310 receives as little as 0.5%. As will be appreciated, such a maldistribution of air flow can lead to deterioration in the performance of the system 100 as there can be stagnation region where heat transfer is minimal. Additionally, such a maldistribution reduces the benefits gained from configurations intended to increase the surface area available for heat exchange.

Accordingly, there is a need for improved heat exchanger devices and systems incorporating configurations and mechanisms to improve air distribution along the heat exchanger tubes.

SUMMARY

Examples of the present disclosure include improved heat exchanger devices and systems. The system can include a first slab of refrigerant tubes and a second slab of refrigerant tubes. The first slab can have (i) an upstream side, (ii) a downstream side, (iii) a linear shaped region, and (iv) a curved region. The second slab can have (i) an upstream side, (ii) a downstream side, (iii) a linear shaped region, and (iv) a curved region. The linear region of the first slab can be closer to the upstream side of the first slab and the curved region of the first slab can be closer to the downstream side of the first slab. Further, the linear shaped region of the second slab can be closer to the upstream side of the second slab and the curved region of the second slab can be closer to the downstream side of the second slab. The downstream side of first slab can be set apart a first distance from the downstream side of the second slab and the upstream side of the first slab can be set apart a second distance from the upstream side of the second slab. Additionally, the second distance can be greater than the first distance.

Further, the heat exchanger system can include a third slab of refrigerant tubes, the third slab having (i) an upstream side, (ii) a downstream side, (iii) a linear shaped region, and (iv) a curved region. The linear shaped region of the third slab can be closer to the upstream side of the third slab and the curved region of the third slab can be closer to the downstream side of the third slab. Further, the downstream side of third slab can be set apart a third distance from the downstream side of one of the first or second slabs and the upstream side of the third slab can be set apart a fourth distance from the upstream side of the slab of the first or second slabs. The third distance can be greater than the fourth distance.

A further example of the present disclosure can provide a heat exchanger system where the first slab of refrigerant tubes can be subdivided into a first group of tubes closer to the upstream side of the first slab and a second group of tubes closer to the downstream side of the first slab. The second slab of refrigerant tubes can be subdivided into a third group of tubes closer to the upstream side of the second slab and a fourth group of tubes close to the downstream side of the second slab. The third slab of refrigerant tubes can be subdivided into a fifth group of tubes closer to the upstream side of the third slab and a sixth group of tubes close to the downstream side of the third slab.

An additional example of the present disclosure can provide a heat exchanger system where the number of tubes in the first group of tubes can be greater than the number of tubes in the second group of tubes, the number of tubes in the third group of tubes can be greater than the number of tubes in the fourth group of tubes, and the number of tubes in the fifth group of tubes can be greater than the number of tubes in the sixth group of tubes.

A further example of the present disclosure can provide a heat exchanger system where the diameter of each tube in the first group of tubes can be greater than diameter of each tube in the second group of tubes, the diameter of each tube in the third group of tubes can be greater than diameter of each tube in the fourth group of tubes, and the diameter of each tube in the fifth group of tubes can be greater than the diameter of each tube in the sixth group of tubes.

These and other aspects, objects, features, and embodiments will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and which are incorporated into and constitute a portion of this disclosure, illustrate various implementations and aspects of the disclosed technology and, together with the description, serve to explain the principles of the disclosed technology. In the drawings:

FIG. 1 is an example of a prior art heat exchanger system.

FIGS. 2A and 2B are examples of prior art slabs of HX tubes.

FIGS. 3A and 3B are charts depicting simulation results of a prior art heat exchanger system having slabs as shown in FIG. 2A.

FIGS. 4A, 4B, and 4C are schematic views of example geometric layouts for slabs of HX tubes, in accordance with the present disclosure.

FIGS. 5A, 5B, 5C and 5D are schematic views of examples slabs of HX tubes, in accordance with the present disclosure.

FIGS. 6A and 6B are schematic views of examples slabs of HX tubes of varying dimension, in accordance with the present disclosure.

FIGS. 7A and 7B are schematic views of examples slabs of microchannel HX tubes of varying dimension, in accordance with the present disclosure.

FIG. 8A is a schematic view of examples slabs of HX tubes having air distribution devices, in accordance with the present disclosure.

FIG. 8B is a schematic view of an example air distribution device for use with heat exchanger slabs, in accordance with the present disclosure.

FIG. 9 is a schematic view of an example heat exchanger system having air distribution devices, in accordance with the present disclosure.

FIG. 10A is a schematic view of an example heat exchanger system having air distribution devices, in accordance with the present disclosure.

FIG. 10B-10D are charts depicting simulation results of the heat exchanger system having air distribution devices as shown in FIG. 10A.

FIG. 11A is a schematic of a conventional heat exchanger drain pan.

FIGS. 11B-11D are schematics views of example heat exchanger drain pans, in accordance with the present disclosure.

FIGS. 12A-12D are charts depicting simulation results of a heat exchanger system incorporating the heat exchanger drain pans shown in FIGS. 11A-11D.

FIG. 13 is a schematic view of a fin and coil assembly for use in example heat exchanger systems, in accordance with the present disclosure.

It is noted that the drawings of the disclosure are not to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION

Disclosed are improved heat exchanger devices and systems incorporating configurations and mechanisms to improve air distribution along the heat exchanger tubes.

Some example implementations of the disclosed technology will be described more fully with reference to the accompanying drawings. This disclosed technology may, however, be embodied in many different forms and should not be construed as limited to the implementations set forth herein. The components described hereinafter as making up various elements of the disclosed technology are intended to be illustrative and not restrictive. Many suitable components that would perform the same or similar functions as components described herein are intended to be embraced within the scope of the disclosed electronic devices and methods. Such other components not described herein may include, but are not limited to, for example, components developed after development of the disclosed technology.

Herein, the use of terms such as “having,” “has,” “including,” or “includes” are open-ended and are intended to have the same meaning as terms such as “comprising” or “comprises” and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as “can” or “may” are intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.

By “comprising” or “containing” or “including” is meant that at least the named compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

It is also to be understood that the mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified.

The components described hereinafter as making up various elements of the disclosure are intended to be illustrative and not restrictive. Many suitable components that would perform the same or similar functions as the components described herein are intended to be embraced within the scope of the disclosure. Such other components not described herein can include, but are not limited to, for example, similar components that are developed after development of the presently disclosed subject matter.

Reference will now be made in detail to example embodiments of the disclosed technology, examples of which are illustrated in the accompanying drawings and disclosed herein. Throughout this disclosure, reference is made to the downstream and upstream directions. Unless otherwise indicated, the upstream direction is depicted in the drawings as generally downward, and the downstream direction is depicted in the drawings as generally upward.

FIG. 4A is a schematic view of an example heat exchange systems 400 including improved geometric layouts for slabs of HX tubes, in accordance with the present disclosure. As shown in FIG. 4A, heat exchange system 400 can include a heat exchanger 410 and a blower 420. Heat exchanger 410 can include a first curved slab of HX tubes 402, a second curved slab of HX tubes 404, and a third curved slab of HX tubes 406. As depicted, each slab 402, 404, 406 can include an upstream side, a downstream side, a linear shaped region, and a curved region.

As further shown, the linear region of the first slab 402 can be closer to the upstream side of the first slab 402, and the curved region of the first slab 402 can be closer to the downstream side of the first slab 403. Additionally, the linear region of the second slab 404 can be closer to the upstream side of the second slab 404, and the curved region of the second slab 404 can be closer to the downstream side of the second slab 404. Further, the linear region of the third slab 406 can be closer to the upstream side of the third slab 406, and the curved region of the third slab 406 can be closer to the downstream side of the third slab 406. The downstream side of first slab 402 can be set apart a first distance from the downstream side of the second slab 404, and the upstream side of the first slab 402 can be set apart a second distance from the upstream side of the second slab 404. As further depicted, the downstream side of third slab 406 can be set apart a third distance from the downstream side of one of the first or second slabs 402, 404, and the upstream side of the third slab 406 can be set apart a fourth distance from the upstream side of the slab of the first or second slabs 402, 404. Such a geometric alignment results in an “N” shape having an enlarged region between slabs due to the presence of the curves. As will be appreciated, such a design increases the flow area and helps prevent the development of a high velocity region.

FIG. 4B is a schematic view of an example heat exchange systems 400 including improved geometric layouts for slabs of HX tubes, in accordance with the present disclosure. As shown in FIG. 4B, heat exchange system 400 can include a heat exchanger 410 and a blower 420. Heat exchanger 410 can include a first slab of HX tubes 401, a second slab of HX tubes 403, and a third slab of HX tubes 405. As depicted, each slab 401, 403, 405 can include an upstream side and a downstream side.

As further shown, the downstream side of first slab 401 can be set apart a first distance from the downstream side of the second slab 405. The upstream side of the first slab 401 can be set apart a second distance from the upstream side of the second slab 405. The second distance can be greater than the first distance such that the first and second slabs 401, 405 angle inwardly in the direction of flow. The upstream side of the first slab 401 can be attached to the first side of the third slab 403, and the upstream side of the second slab 405 can be attached to the second side of the third slab 403. Such a geometric alignment results in an “A” shape having an enlarged region between slabs due to the presence of the curves. As will be appreciated, such a design increases the flow area and prevents the development of a high velocity region. Further, the trapezoid shape with a tilted surface of the slabs 401, 403, 405 can allow condensate drain down along the slabs 401, 403, 405.

FIG. 4C is a schematic view of an example heat exchange systems 400 including improved geometric layouts for slabs of HX tubes, in accordance with the present disclosure. As shown in FIG. 4C, heat exchange system 400 can include a heat exchanger 410 and a blower 420. Heat exchanger 410 can include a first slab of HX tubes 408, a second slab of HX tubes 412, and a third slab of HX tubes 411. As depicted, first and second slabs 408, 412 can each include an upstream side and a downstream side, and third slab 411 can include a first side and a second side. Further, third slab 411 can be a curved slab having a curved region located between the first and second slides. The curved slab can be concave in the direction of flow, as shown in FIG. 4C. Alternatively, the curved slab can be convex in the direction of flow. The downstream side of first slab 408 can be set apart a first distance from the downstream side of the second slab 412. The upstream side of the first slab 408 can be set apart a second distance from the upstream side of the second slab 412. The second distance can be greater than the first distance such that the first and second slabs 408, 412 angle inwardly in the direction of flow. Additionally, the upstream side of the first slab 408 can be attached to the first side of the third slab 411, and the upstream side of the second slab 412 can be attached to the second side of the third slab 411. Such a geometric alignment results in an “A” shape having an enlarged region between slabs due to the presence of the curves. As will be appreciated, such a design increases the flow area and prevents the development of a high velocity region.

FIG. 5A is a schematic view of an example heat exchanger 500 having varying numbers of HX tubes along the slabs, in accordance with an example of the present disclosure. As shown in FIG. 5A, heat exchanger 500 can include a first slab 510, a second slab 520, and a third slab 530. As further shown, the first 510, second 520, and third slabs 530 can be oriented to form an “N” shape as previously described. The first slab 510 can include a first region 512 having a first plurality of HX tubes 513 a, 513 b, 513 c and a second region 514 having a second plurality of HX tubes 515 a, 515 b, 515 c. The second slab 520 can include a first region 522 having a first plurality of HX tubes 523 a, 523 b, 523 c and a second region 524 having a second plurality of HX tubes 525 a, 525 b, 525 c. The third slab 530 can include a first region 532 having a first plurality of HX tubes 533 a, 533 b, 533 c and a second region 534 having a second plurality of HX tubes 535 a, 535 b, 535 c.

As further depicted, the first region 512 can be closer to the upstream side of the first slab 510 and the second region 514 can be closer to the downstream side of the first slab 510. The number of HX tubes in the first plurality of HX tubes 513 a, 513 b, 513 c can be less than the number of HX tubes in the second plurality of HX tubes 515 a, 515 b, 515 c. Further, the first region 522 can be closer to the upstream side of the first slab 520 and the second region 524 can be closer to the downstream side of the first slab 520. The number of HX tubes in the first plurality of HX tubes 523 a, 523 b, 523 c can be less than the number of HX tubes in the second plurality of HX tubes 525 a, 525 b, 525 c. Further, the first region 532 can be closer to the upstream side of the first slab 530, and the second region 534 can be closer to the downstream side of the first slab 530. The number of HX tubes in the first plurality of HX tubes 533 a, 533 b, 533 c can be less than the number of HX tubes in the second plurality of HX tubes 535 a, 535 b, 535 c. As will be appreciated, having fewer tubes in the region of the slabs 510, 520, 530 with lower airflow will reduce the resistance in the lower airflow region therefore improving the airflow distribution of the heat exchanger system 500. As will be further appreciated, both the number and orientation of the HX tubes can be varied based on the airflow of the system 500.

FIG. 5B is a schematic view of an example heat exchanger 500 having varying numbers of HX tubes along the slabs, in in accordance with an example of the present disclosure. As shown in FIG. 5B, heat exchanger 500 can include a first slab 510 and a second slab 520. As further shown, the first slab 510 and second slab 520 can be oriented to form an “A” shape as previously described. The first slab 510 can include a first region 512 having a first plurality of HX tubes 513 a, 513 b, 513 c and a second region 514 having a second plurality of HX tubes 515 a, 515 b, 515 c. The second slab 520 can include a first region 522 having a first plurality of HX tubes 523 a, 523 b, 523 c and a second region 524 having a second plurality of HX tubes 525 a, 525 b, 525 c.

As further depicted, the first region 512 can be closer to the upstream side of the first slab 510, and the second region 514 can be closer to the downstream side of the first slab 510. The number of HX tubes in the first plurality of HX tubes 513 a, 513 b, 513 c can be less than the number of HX tubes in the second plurality of HX tubes 515 a, 515 b, 515 c. Further, the first region 522 can be closer to the upstream side of the first slab 520, and the second region 524 can be closer to the downstream side of the first slab 520. The number of HX tubes in the first plurality of HX tubes 523 a, 523 b, 523 c can be less than the number of HX tubes in the second plurality of HX tubes 525 a, 525 b, 525 c. As will be appreciated, having fewer tubes in the region of the slabs 510, 520 with lower airflow will reduce the resistance in the lower airflow region therefore improving the airflow distribution of the heat exchanger system 500. As will be further appreciated, both the number and orientation of the HX tubes can be varied based on the airflow of the system 500.

FIG. 5C is a schematic view of an example heat exchanger 500 having varying numbers of HX tubes along the slabs, in accordance with an example of the present disclosure. As shown in FIG. 5C, heat exchanger 500 can include a first slab 510, a second slab 520, and a third slab 530. As further shown, the first 510, second 520, and third slabs 530 can be oriented to form an “N” shape as previously described. The first slab 510 can include a first region 512 having a first plurality of HX tubes 513 a, 513 b, 513 c, a second region 514 having a second plurality of HX tubes 515 a, 515 b, 515 c, and a third region 516 having a second plurality of HX tubes 517 a, 517 b, 517 c. The second slab 520 can include a first region 522 having a first plurality of HX tubes 523 a, 523 b, 523 c, a second region 524 having a second plurality of HX tubes 525 a, 525 b, 525 c, and a third region 526 having a third plurality of HX tubes 527 a, 527 b, 527 c. The third slab 530 can include a first region 532 having a first plurality of HX tubes 533 a, 533 b, 533 c, a second region 534 having a second plurality of HX tubes 535 a, 535 b, 535 c, and a third region 536 having a third plurality of HX tubes 537 a, 537 b, 537 c.

As further depicted, the first region 512 can be closer to the upstream side of the first slab 510, the third region 516 can be closer to the downstream side of the first slab 510, and the second region 514 can be between the first region 512 and the third region 516. The number of HX tubes in the first plurality of HX tubes 513 a, 513 b, 513 c can be less than the number of HX tubes in the second plurality of HX tubes 515 a, 515 b, 515 c. Additionally, the number of HX tubes in the second plurality of HX tubes 515 a, 515 b, 515 c can be less than the number of HX tubes in the third plurality of HX tubes 517 a, 517 b, 517 c. Further, the first region 522 can be closer to the upstream side of the first slab 520, the third region 526 can be closer to the downstream side of the first slab 520, and the second region 524 can be between the first region 522 and the third region 526. The number of HX tubes in the first plurality of HX tubes 523 a, 523 b, 523 c can be less than the number of HX tubes in the second plurality of HX tubes 525 a, 525 b, 525 c. Additionally, the number of HX tubes in the second plurality of HX tubes 525 a, 525 b, 525 c can be less than the number of HX tubes in the third plurality of HX tubes 527 a, 527 b, 527 c. Further, the first region 532 can be closer to the upstream side of the first slab 530, the third region 536 can be closer to the downstream side of the first slab 530, and the second region 534 can be between the first region 532 and the third region 536. The number of HX tubes in the first plurality of HX tubes 533 a, 533 b, 533 c can be less than the number of HX tubes in the second plurality of HX tubes 535 a, 535 b, 535 c. Additionally, the number of HX tubes in the second plurality of HX tubes 535 a, 535 b, 535 c can be less than the number of HX tubes in the third plurality of HX tubes 537 a, 537 b, 537 c. As will be appreciated, having fewer tubes in the regions of the slabs 510, 520, 530 with lower airflow will reduce the resistance in the lower airflow region therefore improving the airflow distribution of the heat exchanger system 500. As will be further appreciated, both the number and orientation of the HX tubes can be varied based on the airflow of the system 500.

FIG. 5D is a schematic view of an example heat exchanger 500 having varying numbers of HX tubes along the slabs, in in accordance with an example of the present disclosure. As shown in FIG. 5D, heat exchanger 500 can include a first slab 510 and a second slab 520. As further shown, the first and second slabs 510, 520 can be oriented to form an “A” shape as previously described. The first slab 510 can include a first region 512 having a first plurality of HX tubes 513 a, 513 b, 513 c, a second region 514 having a second plurality of HX tubes 515 a, 515 b, 515 c, and a third region 516 having a second plurality of HX tubes 517 a, 517 b, 517 c. The second slab 520 can include a first region 522 having a first plurality of HX tubes 523 a, 523 b, 523 c, a second region 524 having a second plurality of HX tubes 525 a, 525 b, 525 c, and a third region 526 having a third plurality of HX tubes 527 a, 527 b, 527 c.

As further depicted, the first region 512 can be closer to the upstream side of the first slab 510, the third region 516 can be closer to the downstream side of the first slab 510, and the second region 514 can be between the first region 512 and the third region 516. The number of HX tubes in the first plurality of HX tubes 513 a, 513 b, 513 c can be less than the number of HX tubes in the second plurality of HX tubes 515 a, 515 b, 515 c. Additionally, the number of HX tubes in the second plurality of HX tubes 515 a, 515 b, 515 c can be less than the number of HX tubes in the third plurality of HX tubes 517 a, 517 b, 517 c. Further, the first region 522 can be closer to the upstream side of the first slab 520, the third region 526 can be closer to the downstream side of the first slab 520, and the second region 524 can be between the first region 522 and the third region 526. The number of HX tubes in the first plurality of HX tubes 523 a, 523 b, 523 c can be less than the number of HX tubes in the second plurality of HX tubes 525 a, 525 b, 525 c. Additionally, the number of HX tubes in the second plurality of HX tubes 525 a, 525 b, 525 c can be less than the number of HX tubes in the third plurality of HX tubes 527 a, 527 b, 527 c. As will be appreciated, having fewer tubes in the regions of the slabs 510, 520, 530 with lower airflow will reduce the resistance in the lower airflow region therefore improving the airflow distribution of the heat exchanger system 500. As will be further appreciated, both the number and orientation of the HX tubes can be varied based on the airflow of the system 500.

FIG. 6A is a schematic view of an example heat exchanger 600 having HX tubes of varying dimension along the slabs, in in accordance with an example of the present disclosure. As shown in FIG. 6A, heat exchanger 600 can include a first slab 610, a second slab 620, and a third slab 630. As further shown, the first, second, and third slabs 610, 620, 630 can be oriented to form an “N” shape as previously described. The first slab 610 can include a first region 612 having a first plurality of HX tubes 613 a, 613 b, 613 c and a second region 614 having a second plurality of HX tubes 615 a, 615 b, 615 c. The second slab 620 can include a first region 622 having a first plurality of HX tubes 623 a, 623 b, 623 c and a second region 624 having a second plurality of HX tubes 625 a, 625 b, 625 c. The third slab 630 can include a first region 632 having a first plurality of HX tubes 633 a, 633 b, 633 c and a second region 634 having a second plurality of HX tubes 635 a, 635 b, 635 c.

As further depicted, the first region 612 can be closer to the upstream side of the first slab 610, and the second region 614 can be closer to the downstream side of the first slab 610. The diameter of each HX tube in the first plurality of HX tubes 613 a, 613 b, 613 c can be less than the diameter of each HX tube in the second plurality of HX tubes 615 a, 615 b, 615 c. Further, the first region 622 can be closer to the upstream side of the first slab 620 and the second region 624 can be closer to the downstream side of the first slab 620. The diameter of each HX tube in the first plurality of HX tubes 623 a, 623 b, 623 c can be less than the diameter of each HX tube in the second plurality of HX tubes 625 a, 625 b, 625 c. Further, the first region 632 can be closer to the upstream side of the first slab 630 and the second region 634 can be closer to the downstream side of the first slab 630. The diameter of each HX tube in the first plurality of FIX tubes 633 a, 633 b, 633 c can be less than the diameter of each HX tube in the second plurality of HX tubes 635 a, 635 b, 635 c. As will be appreciated, having tubes with smaller diameters in the region of the slabs 610, 620, 630 with lower airflow will reduce the resistance in the lower airflow region therefore improving the airflow distribution of the heat exchanger system 600. As will be further appreciated, both the number and orientation of the HX tubes can be varied based on the airflow of the system 600.

FIG. 6B is a schematic view of an example heat exchanger 600 having HX tubes of varying dimension along the slabs, in in accordance with an example of the present disclosure. As shown in FIG. 6B, heat exchanger 600 can include a first slab 610 and a second slab 620. As further shown, the first and second slabs 610, 620 can be oriented to form an “A” shape as previously described. The first slab 610 can include a first region 612 having a first plurality of HX tubes 613 a, 613 b, 613 c and a second region 614 having a second plurality of HX tubes 615 a, 615 b, 615 c. The second slab 620 can include a first region 622 having a first plurality of HX tubes 623 a, 623 b, 623 c and a second region 624 having a second plurality of HX tubes 625 a, 625 b, 625 c.

As further depicted, the first region 612 can be closer to the upstream side of the first slab 610 and the second region 614 can be closer to the downstream side of the first slab 610. The diameter of each HX tube in the first plurality of HX tubes 613 a, 613 b, 613 c can be less than the diameter of each HX tube in the second plurality of HX tubes 615 a, 615 b, 615 c. Further, the first region 622 can be closer to the upstream side of the first slab 620 and the second region 624 can be closer to the downstream side of the first slab 620. The diameter of each HX tube in the first plurality of HX tubes 623 a, 623 b, 623 c can be less than the diameter of each HX tube in the second plurality of HX tubes 625 a, 625 b, 625 c. As will be appreciated, having tubes with smaller diameters in the region of the slabs 610, 620 with lower airflow will reduce the resistance in the lower airflow region therefore improving the airflow distribution of the heat exchanger system 600. As will be further appreciated, both the number and orientation of the HX tubes can be varied based on the airflow of the system 600.

While various examples are described herein as having holes with a diameter (e.g., a circular hole), the holes can be of any shape and dimension. For example, one, some, or all of the holes for a particular slab can have a shape that is circular, ovular, square, rectangular, trapezoidal, polygonal, elliptical, triangular, irregular, or the like.

FIG. 7A is a schematic view of an example heat exchanger 700 having microchannel HX tubes of varying dimension along the slabs, in accordance with an example of the present disclosure. As shown in FIG. 7A, heat exchanger 700 can include a first slab 710, a second slab 720, and a third slab 730. As further shown, the first, second, and third slabs 710, 720, 730 can be oriented to form an “N” shape as previously described. The first slab 710 can include a first region 712 having a first plurality of microchannel HX tubes 713 a, 713 b, 713 c and a second region 714 having a second plurality of microchannel HX tubes 715 a, 715 b, 715 c. The second slab 720 can include a first region 722 having a first plurality of microchannel HX tubes 723 a, 723 b, 723 c and a second region 724 having a second plurality of microchannel HX tubes 725 a, 725 b, 725 c. The third slab 730 can include a first region 732 having a first plurality of microchannel HX tubes 733 a, 733 b, 733 c and a second region 734 having a second plurality of microchannel HX tubes 735 a, 735 b, 735 c.

As further depicted, the first region 712 can be closer to the upstream side of the first slab 710 and the second region 714 can be closer to the downstream side of the first slab 710. The height and/or width of each microchannel HX tube in the first plurality of microchannel HX tubes 713 a, 713 b, 713 c can be less than the height and/or width of each microchannel HX tube in the second plurality of microchannel HX tubes 715 a, 715 b, 715 c. Further, the first region 722 can be closer to the upstream side of the second slab 720 and the second region 724 can be closer to the downstream side of the second slab 720. The height and/or width of each microchannel HX tube in the first plurality of microchannel HX tubes 723 a, 723 b, 723 c can be less than the height and/or width of each microchannel HX tube in the second plurality of microchannel HX tubes 725 a, 725 b, 725 c. Further, the first region 732 can be closer to the upstream side of the third slab 730 and the second region 734 can be closer to the downstream side of the third slab 730. The height and/or width of each microchannel HX tube in the first plurality of microchannel HX tubes 733 a, 733 b, 733 c can be less than the height and/or width of each microchannel HX tube in the second plurality of microchannel HX tubes 735 a, 735 b, 735 c. As will be appreciated, having tubes with smaller dimensions in the region of the slabs 710, 720, 730 with lower airflow will reduce the resistance in the lower airflow region therefore improving the airflow distribution of the heat exchanger system 700. As will be further appreciated, both the number and orientation of the HX tubes can be varied based on the airflow of the system 700.

FIG. 7B is a schematic view of an example heat exchanger 700 having microchannel HX tubes of varying dimension along the slabs, in in accordance with an example of the present disclosure. As shown in FIG. 7A, heat exchanger 700 can include a first slab 710 and a second slab 720. As further shown, the first and second 710, 720 slabs can be oriented to form an “A” shape as previously described. The first slab 710 can include a first region 712 having a first plurality of microchannel HX tubes 713 a, 713 b, 713 c and a second region 714 having a second plurality of microchannel HX tubes 715 a, 715 b, 715 c. The second slab 720 can include a first region 722 having a first plurality of microchannel HX tubes 723 a, 723 b, 723 c and a second region 724 having a second plurality of microchannel HX tubes 725 a, 725 b, 725 c.

As further depicted, the first region 712 can be closer to the upstream side of the first slab 710 and the second region 714 can be closer to the downstream side of the first slab 710. The height and/or width of each microchannel HX tube in the first plurality of microchannel HX tubes 713 a, 713 b, 713 c can be less than the height and/or width of each microchannel HX tube in the second plurality of microchannel HX tubes 715 a, 715 b, 715 c. Further, the first region 722 can be closer to the upstream side of the second slab 720 and the second region 724 can be closer to the downstream side of the second slab 720. The height and/or width of each microchannel HX tube in the first plurality of microchannel HX tubes 723 a, 723 b, 723 c can be less than the height and/or width of each microchannel HX tube in the second plurality of microchannel HX tubes 725 a, 725 b, 725 c. As will be appreciated, having tubes with smaller dimensions in the region of the slabs 710, 720 with lower airflow will reduce the resistance in the lower airflow region therefore improving the airflow distribution of the heat exchanger system 700. As will be further appreciated, both the number and orientation of the HX tubes can be varied based on the airflow of the system 700.

FIG. 8A is a schematic view of example heat exchanger system 800 having air distribution devices, in accordance with the present disclosure. As shown in FIG. 8A, heat exchanger 800 can include a first slab 810, a second slab 820, a third slab 830, and one or more air distribution device 840 a, 840 b, 840 c. As further shown, the first 810, second 820, and third slabs 830 can be oriented to form an “N” shape as previously described. FIG. 8B is a schematic view of an example air distribution device 840 for use with heat exchanger system 800, in accordance with the present disclosure. As shown, air distribution device 840 can be a perforated plate including a plurality of regions.

For example, and as depicted, air distribution device 840 can include a first region 842, a second region 844, a third region 846, and a fourth region 848. The first region 842 can include a plurality of openings 843 a, 843 b, 843 c having a first dimension (e.g. diameter, width, height, etc.) to allow for air flow through the opening and to a portion of a slab. The second region 844 can include a plurality of openings 845 a, 845 b, 845 c having a second dimension (e.g. diameter, width, height, etc.) to allow for air flow through the opening and to a portion of a slab. The third region 846 can include a plurality of openings 847 a, 847 b, 847 c having a third dimension (e.g. diameter, width, height, etc.) to allow for air flow through the opening and to a portion of a slab. The fourth region 848 can include a plurality of openings 849 a, 849 b, 849 c having a fourth dimension (e.g. diameter, width, height, etc.) to allow for air flow through the opening and to a portion of a slab. As will be appreciated, the shape and dimension of the openings can correspond to the distribution of airflow on the slabs. For example, the larger dimensioned openings can be positioned so as to direct larger portions of airflow onto the upstream portion of the slabs and the smaller dimensioned openings can be positioned so as to direct smaller portions of airflow on the downstream portion of the slabs. While the openings described herein are depicted as circular, the openings can be of any shape and dimension. For example, one, some, or all of the openings for a particular slab can have a shape that is circular, ovular, square, rectangular, trapezoidal, polygonal, elliptical, triangular, irregular, or the like.

FIG. 9 is a schematic view of example heat exchanger system 900 having air distribution devices, in accordance with the present disclosure. As shown in FIG. 9, heat exchanger 900 can include a first slab 910, a second slab 920, a third slab 930, and one or more air distribution devices 940. As further shown, the first 910, second 920, and third slabs 930 can be oriented to form an “N” shape as previously described. As shown, air distribution device 940 can include a plurality of vanes 940 a, 940 b, 940 c, 940 d, 940 e, 940 f, 940 g configured to distributed air to various portions of the slabs 910, 920, 930. As will be appreciated, the orientation of the vanes can correspond to the distribution of airflow on the slabs. For example, the more vanes can be utilized for routing larger portions of airflow onto the upstream portion of the slabs and the less vanes can be positioned so as to direct smaller portions of airflow on the downstream portion of the slabs.

FIG. 10A is a schematic view of example heat exchanger system 1000 having air distribution devices, in accordance with the present disclosure. As shown, the system 100 can include an inlet duct 1002, a heat exchanger 1004, a blower 1006, and an outlet duct 1008. As further shown, heat exchanger 1004 can include a first slab 1010, a second slab 1020, a third slab 1030, and one or more air distribution device 1040 a, 1040 b, 1040 c, 1040 d, 1040 e, 1040 f, 1040 g, 1040 h, 1040 i, 1040 j, 1040 k, 1040 l. The first 1010, second 1020, and third slabs 1030 can be oriented to form an “N” shape as previously described. As depicted, air distribution device 1040 can include a plurality of vanes 1040 a, 1040 b, 1040 c, 1040 d, 1040 e, 1040 f, 1040 g, 1040 h, 1040 i, 1040 j, 1040 k, 1040 l configured to distributed air to various portions of the slabs 1010, 1020, 1030. As will be appreciated, the number, size, and/or orientation of the vanes can correspond to the distribution of airflow on the slabs. For example, a greater number of vanes can be utilized for routing larger portions of airflow onto the upstream portion of the slabs, and a lesser number of vanes can be positioned so as to direct smaller portions of airflow on the downstream portion of the slabs. FIG. 10B-10D are charts depicting simulation results of the heat exchanger system having air distribution devices as shown in FIG. 10A. FIG. 10B depicts the airflow through the first slab 1010. FIG. 10C depicts the airflow through the second slab 1020. FIG. 10D depicts the airflow through the third slab 1030. As shown, all slabs 1010, 1020, 1030 have an airflow distribution that is more uniform than the prior art systems depicted in FIGS. 3A & 3B. As will be appreciated, the reduction in the maldistribution (e.g., as facilitated, at least in part, by the air distribution device 1040) increases the benefits and gained from configurations intended to increase the surface area available for heat exchange.

The maldistribution of airflow can also be reduced by modifications to, or different designs for, the drain pan, which is used for collecting water droplets that drip from a heat exchanger system (e.g., condensate from the heat exchanger coils), such as the ones previously described, and discharging the water droplets external to the system. FIG. 11A is a schematic of a conventional heat exchanger drain pan 1100. As will be appreciated, such systems are designed to prevent water from leaking into electrical components of the system, which can cause system damage and/or failure. As shown, a first portion 1102 a of the drain pain 1100 can be positioned such that it is under a first slab of the heat exchanger system and a second portion 1104 b of the drain pain 1100 can be positioned such that it is under the second and third slabs. As further depicted, first and second portions 1102 a, 1102 b can include receiving portions 1103 a, 1103 b having angled surfaces and lip portions configured to receive water that drips from the heat exchanger system. FIG. 12A is a chart depicting simulation results of a heat exchanger system having the heat exchanger drain pan 1100 shown in FIG. 11A. As shown, the airflow at the bottom of the slabs is greatly reduced as a result of the drain pan blocking airflow.

FIGS. 11B-11D are schematics views of example heat exchanger drain pans, in accordance with the present disclosure. FIG. 11B depicts a schematic of a heat exchanger drain pan 1105 wherein both a first portion 1104 a and a second portion 1104 b include reductions to the lip such that the overall area of the drain pan 1105 is reduced. As shown, both the first and second portions 1104 a, 1104 b have geometries different from traditional drain pans. In particular, the first and second portions 1104 a, 1104 b each have a widest point from which the width of the first or second portion 1104 a, 1104 b tapers inwardly as the distance from the widest point increases. FIG. 12B is a chart depicting simulation results of a heat exchanger system having the heat exchanger drain pan 1105 shown in FIG. 11B. As shown, the airflow at the bottom of the slabs is increased as a result of the reduction in the overall area of the drain pan.

FIG. 11C depicts a schematic of a heat exchanger drain pan 1110 wherein both a first portion 1106 a and a second portion 1106 b include reduced width relative to the typical drain pan 1100 such that the overall area of the drain pan 1110 is reduced. FIG. 12C is a chart depicting simulation results of a heat exchanger system having the heat exchanger drain pan 1110 shown in FIG. 11C. As shown, the airflow at the bottom of the slabs is increased as a result of the reduction in the overall area of the drain pan.

FIG. 11D depicts a schematic of a heat exchanger drain pan 1115 wherein both a first portion 1108 a and a second portion 1108 b include reduced width relative to the typical drain pan 1100. As further depicted, the receiving portion 1109 a, 1109 b include reduced depths (e.g., the portion that receives the water droplets is shallower). As will be appreciated, such a design leads to reductions in the overall area of the drain pan 1115. FIG. 12D is a chart depicting simulation results of a heat exchanger system having multiple vanes, such as those previously described with respect to FIG. 10A, and the heat exchanger drain pan 1115 shown in FIG. 11D. As shown, the airflow at the bottom of the slabs is increased as a result of the reduction in the overall area of the drain pan.

FIG. 13 is a schematic view of a fin and coil assembly 1300 for use in heat exchanger systems, in accordance with the present disclosure. As depicted, fin and coil assembly 1300 can include a base pan 1304, which can be designed similarly to previously described base pans. The base pan 1304 can be oriented under a plurality of coils 1302 a, 1302 b, 1302 c, 1032 d, 1302 e, 1302 f, which can be split into a plurality of coil portions A, B. Each plurality of coil portions A, B can include respective fin coil orientations. For example, fin and coil assembly 1300 can include a first plurality of fins 1306 interdigitated with a second plurality of fins 1308. As shown, the first plurality of fins 1306 can extend the full height of the coil fin and coil assembly 1300 (i.e., through both portions A and B), and the second plurality of fins 1308 can extend only through the top portion A of the coil fin and coil assembly 1300, with the bottom edges 1310 of the vertically shorter fins 1308 being positioned at the upper end of the bottom coil portion B.

As will be appreciated, such a design provides fin and coil assembly 1300 with an effective fin density (and thus an air-to-fin contact area) along the bottom coil portion B, which can be half that in the upper coil portion A. Accordingly, the velocity of the air which is being drawn by a fan or pushed by a blower through the bottom portion B of the fin and coil assembly 1300 can be substantially increased compared to the velocity that it would have in a conventionally configured coil in which the fin density was constant throughout the coil. This configuration of the fin and coil assembly 1300 provides a variety of advantages over conventionally configured coils including, for example, material cost savings, weight reduction, enhanced air side convective heat transfer, improved air velocity profiles, lowered air side pressure drop, improved condensate drainage efficiency, lowered frost and ice accumulation on the coil, and lowered thermal coil stress.

As will also be readily appreciated by those of ordinary skill in this particular art, a variety of modifications could be made to the representatively illustrated fin and coil assembly 1300 without departing from principles of the present invention. For example, only two fin sizes are used in the fin and coil assembly 1300. However, more than two fin sizes could be used, and the fins could be interdigitated in other manners, if desired. Further, fin and coil assembly 1300 has been show with two different portions A, B having different fin density, however more than two regions could exist. Further, while portions A, B are shown as discrete sections of differing fin density, the fin density can gradually change along the entire length of the assembly, as an alternative. Also, principles of the present invention could be advantageously utilized in coils having various geometries and orientations, such as for example, round coils, flat coils, coils which have non-vertical orientations, etc.

As will be appreciated, the examples presented herein have been directed at reducing the resistance of lower airflow region and increasing the distribution of airflow along the slabs in order to increase the performance of the heat exchangers. In addition to the previously discussed designs, the positioning of the blower can be adjusted to alter the distribution of airflow across the slabs. It will be appreciated that while certain examples have been distinctly shown and discussed, combining such examples falls within the scope of the present disclosure. For example, in some examples, a heat exchanger system could incorporate a combination of varying diameter HX tubes as well as varying numbers of rows of tubes.

Any component described in one or more figures herein can apply to any other figures having the same label. In other words, the description for any component of a figure can be considered substantially the same as the corresponding component described with respect to another figure. For any figure shown and described herein, one or more of the components can be omitted, added, repeated, and/or substituted. Accordingly, embodiments shown in a particular figure should not be considered limited to the specific arrangements of components shown in such figure.

In this description, numerous specific details have been set forth. It is to be understood, however, that implementations of the disclosed technology be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description. References to “one embodiment,” “an embodiment,” “some embodiments,” “example embodiment,” “various embodiments,” “one implementation,” “an implementation,” “example implementation,” “various implementations,” “some implementations,” etc., indicate that the implementation(s) of the disclosed technology so described may include a particular feature, structure, or characteristic, but not every implementation necessarily includes the particular feature, structure, or characteristic. Further, repeated use of the phrase “in one implementation” does not necessarily refer to the same implementation, although it may.

Terms such as “first,” “second,” “top,” “bottom,” “left,” “right,” “end,” “back,” “front,” “side”, “length,” “width,” “inner,” “outer,” “above”, “lower”, and “upper” are used merely to distinguish one component (or part of a component or state of a component) from another. Such terms are not meant to denote a preference or a particular orientation unless specified and are not meant to limit embodiments of water heating devices or heat exchangers. In the foregoing detailed description of the example embodiments, numerous specific details are set forth in order to provide a more thorough understanding of the disclosure. However, it will be apparent to one of ordinary skill in the art that the example embodiments can be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

Accordingly, many modifications and other embodiments set forth herein will come to mind to one skilled in the art to which example water heaters pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that example water heaters are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this application. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

1. A heat exchanger comprising: a first slab of refrigerant tubes, the first slab having (i) an upstream side, (ii) a downstream side, (iii) a linear shaped region, and (iv) a curved region, the linear shaped region being disposed closer to the upstream side than the downstream side and the curved region being disposed close to the downstream side than the upstream side; a second slab of refrigerant tubes, the second slab having (i) an upstream side, (ii) a downstream side, (iii) a linear shaped region, and (iv) a curved region, the linear shaped region being disposed closer to the upstream side than the downstream side and the curved region being disposed close to the downstream side than the upstream side, wherein the downstream side of the first slab is set apart a first distance from the downstream side of the second slab and the upstream side of the first slab is set apart a second distance from the upstream side of the second slab, and wherein the second distance is greater than the first distance.
 2. The heat exchanger of claim 1 further comprising: a third slab of refrigerant tubes, the third slab having (i) an upstream side, (ii) a downstream side, (iii) a linear shaped region, and (iv) a curved region, the linear shaped region being disposed closer to the upstream side than the downstream side and the curved region being disposed close to the downstream side than the upstream side, wherein the downstream side of the third slab is set apart a third distance from the downstream side of one of the first or second slabs and the upstream side of the third slab is set apart a fourth distance from the upstream side of one of the first or second slabs, and wherein the third distance is greater than the fourth distance.
 3. The heat exchanger of claim 2, wherein the first slab is subdivided into a first group of tubes closer to the upstream side of the first slab than the downstream side of the first slab and a second group of tubes closer to the downstream side of the first slab than the upstream side of the first slab.
 4. The heat exchanger of claim 3, wherein the second slab is subdivided into a third group of tubes closer to the upstream side of the second slab than the downstream side of the second slab and a fourth group of tubes closer to the downstream side of the second slab than the upstream side of the second slab.
 5. The heat exchanger of claim 4, wherein the third slab is subdivided into a fifth group of tubes closer to the upstream side of the third slab than the downstream side of the third slab and a sixth group of tubes closer to the downstream side of the third slab than the upstream side of the third slab.
 6. The heat exchanger of claim 5, wherein: a number of tubes in the first group of tubes is greater than a number of tubes in the second group of tubes, a number of tubes in the third group of tubes is greater than a number of tubes in the fourth group of tubes, and a number of tubes in the fifth group of tubes is greater than a number of tubes in the sixth group of tubes.
 7. The heat exchanger of claim 5, wherein: a diameter of each tube in the first group of tubes is greater than a diameter of each tube in the second group of tubes, a diameter of each tube in the third group of tubes is greater than a diameter of each tube in the fourth group of tubes, and a diameter of each tube in the fifth group of tubes is greater than a diameter of each tube in the sixth group of tubes.
 8. The heat exchanger of claim 5, wherein the heat exchanger is a microchannel heat exchanger and the first, second, third, fourth, fifth, and sixth groups of tubes comprise flat tubes.
 9. The heat exchanger of claim 8, wherein: a width of each tube in the first group of tubes is greater than a width of each tube in the second group of tubes, a width of each tube in the third group of tubes is greater than a width of each tube in the fourth group of tubes, and a width of each tube in the fifth group of tubes is greater than a width of each tube in the sixth group of tubes.
 10. The heat exchanger of claim 8, wherein: a height of each tube in the first group of tubes is greater than a height of each tube in the second group of tubes, a height of each tube in the third group of tubes is greater than a height of each tube in the fourth group of tubes, and a height of each tube in the fifth group of tubes is greater than a height of each tube in the sixth group of tubes.
 11. A heat exchanger comprising: a first slab of refrigerant tubes, the first slab having (i) an upstream side and (ii) a downstream side; a second slab of refrigerant tubes, the second slab having (i) an upstream side and (ii) a downstream side, a third slab of refrigerant tubes, the second slab having (i) first side and (ii) a second side, wherein the downstream side of the first slab is set apart a first distance from the downstream side of the second slab, wherein the upstream side of the first slab is attached to the first side of the third slab and the upstream side of the second slab is attached to the second side of the third slab.
 12. The heat exchanger of claim 11, wherein the third slab is a curved slab having a curved region located between the first and second sides.
 13. The heat exchanger of claim 11, wherein: the first slab is subdivided into a first group of tubes closer to the upstream side of the first slab than the downstream side of the first slab and a second group of tubes closer to the downstream side of the first slab than the upstream side of the first slab, and the second slab is subdivided into a third group of tubes closer to the upstream side of the second slab than the downstream side of the second slab and a fourth group of tubes closer to the downstream side of the second slab than the upstream side of the second slab.
 14. The heat exchanger of claim 13, wherein: a number of tubes in the first group of tubes is greater than a number of tubes in the second group of tubes, and a number of tubes in the third group of tubes is greater than a number of tubes in the fourth group of tubes.
 15. The heat exchanger of claim 14, wherein: a diameter of each tube in the first group of tubes is greater than a diameter of each tube in the second group of tubes, and a diameter of each tube in the third group of tubes is greater than a diameter of each tube in the fourth group of tubes.
 16. A heat exchanger comprising: a first slab of refrigerant tubes, the first slab having (i) an upstream side and (ii) a downstream side; a second slab of refrigerant tubes, the second slab having (i) an upstream side and (ii) a downstream side; and an airflow distribution device configured to distribute air along the first and second slabs; wherein the downstream side of the first slab is set apart a first distance from the downstream side of the second slab and the upstream side of the first slab is attached to the upstream side of the second slab.
 17. The heat exchanger of claim 16, further comprising: a third slab of refrigerant tubes, the third slab having (i) an upstream side and (ii) a downstream side; wherein the downstream side of the third slab is attached to the downstream side of the second slab and the upstream side of the third slab is set apart a second distance from the upstream side of the second slab, and wherein the airflow distribution device is further configured to distribute air along the third slab.
 18. The heat exchanger of claim 17, wherein: the first slab is subdivided into a first group of tubes closer to the upstream side of the first slab than the downstream side of the first slab and a second group of tubes closer to the downstream side of the first slab than the upstream side of the first slab, the second slab is subdivided into a third group of tubes closer to the upstream side of the second slab than the downstream side of the second slab and a fourth group of tubes closer to the downstream side of the second slab than the upstream side of the second slab, and the third slab is subdivided into a fifth group of tubes closer to the upstream side of the third slab than a downstream side of the third slab and a sixth group of tubes closer to the downstream side of the third slab than the upstream side of the third slab.
 19. The heat exchanger of claim 18, wherein: a number of tubes in the first group of tubes is greater than a number of tubes in the second group of tubes, a number of tubes in the third group of tubes is greater than a number of tubes in the fourth group of tubes, and a number of tubes in the fifth group of tubes is greater than a number of tubes in the sixth group of tubes.
 20. The heat exchanger of claim 18, wherein: a diameter of each tube in the first group of tubes is greater than a diameter of each tube in the second group of tubes, a diameter of each tube in the third group of tubes is greater than a diameter of each tube in the fourth group of tubes, and a diameter of each tube in the fifth group of tubes is greater than a diameter of each tube in the sixth group of tubes. 